Modern integrated circuits (ICs) oftentimes utilize a plurality of voltage sources to provide power to various integrated circuit components. In certain circumstances, it may be advantageous to selectively utilize more than one of these voltage sources to provide a supply voltage for certain IC components, depending on the current power requirements of the component. For instance, a voltage VccAux may be used to provide a supply voltage Vgg to a memory cell array during normal operation, and a voltage Vdd may be used to provide the supply voltage Vgg during a power saving mode in which the number of reads and writes to the memory cell array are minimal.
Even though the voltage level of VccAux may be higher than that required for the memory cell array, a power supply regulator can be used to generate the appropriate supply voltage Vgg from VccAux. Moreover, the higher voltage level of VccAux provides margin for the power supply regulator to dynamically compensate for voltage drops which often occur when heavy current loads are encountered. Thus VccAux can be used to maintain the voltage level of the supply voltage Vgg relatively constant, even when the load current varies.
By comparison, if the voltage source Vdd is used to provide the supply voltage Vgg, and the nominal voltage level of Vdd is that which is required of the supply voltage Vgg, power regulation need not be applied to the voltage Vdd. Thus, the use of the voltage Vdd to provide the supply voltage Vgg can be more energy efficient than using VccAux and a power regulator. Notwithstanding, the voltage Vdd may not be suitable when the load current is high. For example, a high level of load current may result in a voltage drop that causes the supply voltage Vgg to fall below a suitable voltage level.